DECOMPOSITION IN THE AIR. 261 



painted with white lead was turned black in a 

 single night by clearing out the drains, and so 

 setting free a large quantity of sulphuretted 

 hydrogen. In his day, Sir Kenelm Digby 

 complained much of the odours of the streets, 

 and declared that silver could not be kept 

 clean, an effect due to the agency of this gas. 

 It is often combined with or accompanied by 

 ammonia, which neutralizes its bad effects in 

 some degree. It is also probably oxidized and 

 decomposed by the effects of ozone. 



In addition to these occasional ingredients, 

 it has been supposed by various writers, that, 

 in the words of Dr. Prout, before quoted, " the 

 atmosphere contains a little of everything that 

 is capable of assuming the gaseous shape." In 

 a recent work on science the same statement 

 is repeated in the following words : "A thou- 

 sand results daily and hourly accumulating as 

 truths around us, prove that the solid metals, 

 the gross earths, and the constituents of animal 

 and vegetable life, all pass away invisible to us, 

 and become ' thin air.' We know that, floating 

 around us, these volatilized bodies exist in 

 some form or other." The same idea prevailed 

 in the minds of the ancients,* and is repeated 

 in the following expression of Shakspeare 

 " We must all part into this sea of air." 



* Quodcumque fluit de rebus, id omne 

 Aeris in magnum fertur mare. Lucretius, De Rer. Natitr. 



